Considerable work has been expended in improving techniques for bonding semiconductor integrated circuit chips to conductive circuit patterns of a substrate. One such method uses an anisotropically conductive adhesive between bonding pads on the substrate and matching bonding pads of the integrated circuit chip. The adhesive may typically be an insulative polymer containing conductive particles that simultaneously contact a pad of the chip and a matching pad of the substrate to provide interconnection. The conductive particles do not conduct in the lateral or horizontal direction; since they transmit current only in the vertical direction between the substrate and device bonding pads, the conduction is referred to as "anisotropic." The polymer is cured after mounting the chip on the substrate which thereafter provides a permanent structural bond in addition to a conductive interconnection. The replacement of solder bond connections by anisotropic conductive adhesives can often reduce assembly costs, can accommodate relatively high densities of conductive interconnections, and can make devices more amenable to repair and recycling.
A class of anisotropic conductors that provides a temporary interconnection between a device and a substrate is known as elastomeric conductive polymer interconnection (ECPI) material. This material is useful for interconnecting an electronic device to a test fixture so that current can be appropriately directed through the chip for testing purposes, with the device thereafter being removed from the test fixture. Whether the use is as an ECPI material or an adhesive, anisotropic conductive materials that are used for interconnections to integrated circuit chips must have an appropriately small separation, or pitch, between adjacent conductors so that one can assure that each of the tiny conductor pads of the device will be contacted, and yet the adjacent conductors cannot be so close as to provide lateral conduction or to permit any electrical breakdown within the insulative material. Accordingly, there is a continuing need for anisotropic conductive materials that have a sufficiently small pitch that they can dependably be used to make contact with tiny conductors of an integrated circuit chip and yet are dependable in providing insulation between adjacent conductors of an integrated circuit chip. There is a need for such anisotropic conductors, both for permanently bonding integrated circuit chips to substrates, and for permitting temporary interconnection as is required for device testing.